Rotary web-type offset printing machines, for example offset printing machines used for newspaper printing or the like, frequently have printing couples constructed in four-cylinder form. Two plate cylinders cooperate with two blanket cylinders, the blanket cylinders being positioned to pass a continuous web of paper therebetween and, at the same time, printing prime and verso subject matter. The printing couples are customarily located on a frame which, in general, has an inverted U or inverted channel configuration, and, therefore, such machines or the printing units thereof are also referred to as U-units. In essence, two vertical legs are connected by a bridge element. In the upper part of the bridge, two rubber blanket cylinders are journalled, located with their axes in a horizontal plane. The printing machine units are constructed in mirror-image form. The blanket cylinders simultaneously print on the prime and verso side of the web which is carried vertically therebetween. The plate cylinders are likewise located in horizontal alignment, below the blanket cylinders and, for example, outside and somewhat laterally therefrom. The dampers for the printing units are located inwardly of the plate cylinders. Access to the dampers is impaired since the narrow gap in the middle of the side walls is accessible only with difficulty. During operation, the web runs vertically in the middle of the gap between the legs. Maintenance on the dampers is thus possible only after severing the web. This increases the time and paper loss merely to permit maintenance or other work on the dampers, and eventually requires re-threading of the paper web.
Some printing machines also have their inkers located in positions inwardly of the plate cylinders.